Nal(TI)

Sodium Iodide Detectors

Of all available scintillators, NaI(Tl) is the most extensively used. The material has an unequalled high light output and an excellent match of the emission spectrum to the sensitivity of photomultiplier tubes, resulting in very good energy resolution detectors.

Properties

Material – NaI(Tl)
Density (g/cm3) – 3.67
Emission Maximum (nm) – 415
Thermal expansion coefficient (c^-1) – 47.4 x 10^-6
Decay Constant – 0,23 µs
Refractive Index – 1.85
Conversion Efficiency – 100
Light yield (photons/KeVγ) – 38
Hygroscopic – Yes

NaI(Tl) produces one of the highest signals in a PMT per amount of radiation absorbed. Under optimum conditions, an average of 1x 104 photoelectrons are produced per MeV g-rays. The relation between the scintillation intensity and the temperature is shown in Figure 2 for two main amplifier shaping times. For most applications, a 1 µs shaping time is used for temperatures around room temperature and above. The small difference in PH between the 1 µs and 12 µs shaping times does not affect energy resolution for these temperatures.

NaI(Tl) exhibits several decay time constant components. The primary single exponential decay constant is 250ns at room temperature. As the temperature increases, the longer time constant components decrease in intensity and the 1 µs and 12 µs response curves become identical.

NaI(Tl) is susceptible to radiation damage, i.e. prolonged exposure to intense radiation degrades the scintillation performance. Radiation damage has been observed above levels of 1 Gray (102 rad). The crystal should not be exposed to ultraviolet radiation from fluorescent lamps or sunlight.

Features

Very high light output, good energy resolution

Uses

General scintillation counting, Medical, Security, Industrial, Environmental monitoring, Oil & gas - core logging, Nuclear physics

Applications

Medical – SPECT (gamma camera), whole body counting, radioimmunoassay (RIA)
Security – Thermal neutron activation
Industrial – Thickness or density gauging, coal / mineral assy
Oil and gas exploration – well logging
Environmental monitoring
Aerial survey
Nuclear physics

Further Information

NaI(Tl) crystals are widely used for radiation detection: in nuclear medicine, for environmental monitoring, in nuclear physics, aerial survey, well logging and in many other applications including low background applications.

NaI(Tl) produces one of the highest signals in a PMT per amount of radiation absorbed. Under optimum conditions, an average of 1x 10⁴ photoelectrons are produced per MeV γ-rays.

NaI(Tl) exhibits several decay time constant components. The primary single exponential decay constant is 250ns at room temperature.

NaI(Tl) is susceptible to radiation damage, i.e. prolonged exposure to intense radiation degrades the scintillation performance. Radiation damage has been observed above levels of 1 Gray (10² rad). The crystal should not be exposed to ultraviolet radiation from fluorescent lamps or sunlight.